The Conficker Internet worm could strike at infected computers around the world on April 1, a security expert warned Monday.

Conficker is a sophisticated piece of malicious computer software, or malware, that installs itself on a Windows PC's hard drive via specially written Web pages. It then conceals itself on a computer.

Graham Cluley of the British security firm Sophos confirmed that Conficker is programmed "to hunt for new instructions on April 1."

However, he added, "This does not mean that anything is going to happen, or that the worm is actually going to do anything. Simply, it is scheduled to hunt a wider range of Web sites for instructions on that date."

One strange thing about Conficker is that no one yet has any idea what it is programmed to do.

In February, Cluley told The Times: "It's as if someone is assembling an army of computers around the world, but hasn't yet decided where to point them."

A worst-case scenario for April 1 would be for all the world's millions of infected computers to receive simultaneous instructions to attack, or to flood the Internet with spam e-mail.

Ed Gibson, Microsoft's chief security adviser for the U.K., was reluctant to make predictions about Conficker's behavior.

"April 1 is a classic date for anything like this to go off," he said. "But I really would hate to say that April 1 is going to be unlike any other day."